The present invention relates to a power supply for a vehicle.
Japanese Patent Application Publication No. H10-184506 discloses a power supply for a vehicle having two storage batteries including a lead battery and an additional storage battery.
However, such a power supply having two storage batteries has a problem in that the power supply is difficult to operate according to the characteristics of the respective storage devices.
A power supply, for example for a vehicle, is required to perform such functions as power supply to an auxiliary device, power supply to a starter, powering operation for a motor generator, regenerative operation when voltage of a lead battery is higher than its upper limit voltage (e.g. 14.4V). The control of such operations depends on a load and the characteristics of the respective storage devices. Specifically, the load of a vehicle includes an auxiliary device, a starter, and an alternator and the power input and output requirements are varied with the respective loads operated according to the vehicle requirements. Furthermore, the ranges of the input and output requirements are different according to the characteristics of the respective storage batteries and therefore, it has been difficult for the power supply to provide optimum operation under varying conditions of a vehicle.
For example, a lead battery which is used to supply electric power to a starter has problems in the durability and failure of power supply to an auxiliary device.
Although there is available a single battery that can handle various loads such as an idling stop lead battery, such a battery is costly.
The present invention which has been made in light to the above problems is directed to providing a power supply for a vehicle having a plurality of storage devices including a lead battery that operates appropriately according to the characteristics of the respective storage devices.